BLAST PROTECTION PANEL

Abstract

 In an aspect of the invention there is provided a blast protection panel, comprising a package of fibre-reinforced resin sheets, each sheet having a dominant unidirectional fibre orientation, said package of fibre-reinforced resin sheets formed in packed stacks, each stack comprising at least four fibre-reinforced resin sheets with dominant unidirectional fibres oriented, within said each stack, alternatingly at about right angles relative to each other; and said each stack packed against adjacent stacks, said adjacent stacks comprising sheets with dominant unidirectional fibres oriented at acute angles relative said each stack thereby forming a delamination interface.

Description

FIELD

[0001] The present invention relates to a blast protection panel formed separately or integrally to a compartment, e.g. vehicle compartment, for protecting persons.

BACKGROUND

[0002] In modern defense operations, a desire exists to provide lightweight materials that are yet comparable or better in protective properties when protecting against a blast from e.g. an explosive device such as land mine or improvised explosive devices. Land-based military operations rely heavily on the safety, design and operational capabilities of military vehicles. Because of this, the aforementioned aspects are continuously optimized. The safety of a military vehicle is mainly determined by its ability to withstand threats such as ballistic impact of projectiles and fragments, as well as the structural response to blast loading of mines or IED's. Currently, military vehicles that can withstand a mine/IED blast are typically designed around an underbelly made of thick steel, sometimes with V-shaped form. Such blast protection measures add significant weight to a vehicle, therefore reducing its mobility and off-road capabilities.

[0003] Composite materials, e.g. materials comprising e.g. mixture of resin and (carbon/glass) fibres, and potentially metal sheets, are widely used in the aerospace, marine and automotive industry, where weight reduction, versus improved tensile strength of materials renders large gains. However, in the military, composite materials have yet to be developed that are sufficiently resistant against the extreme loads that develop e.g. during high impact situations, such as explosions. The material of choice there is typically steel or aluminum. The perfect trade-off for blast protection is reached when a more lightweight material with excellent blast resistant capability is used e.g. in a vehicle underbelly.

SUMMARY

[0004] In an aspect of the invention there is provided the features listed in claims 1. In particular, a blast protection panel comprises a package of fibre-reinforced resin sheets, each sheet having a dominant unidirectional fibre orientation, said package of fibre-reinforced resin sheets formed in packed stacks consisting of at least 4 sheets each stack comprising fibre-reinforced resin sheets with fibres oriented, within said each stack, alternatingly at about right angles relative to each other; and said each stack packed against an adjacent stack, said adjacent stacks comprising sheets with dominant unidirectional fibres oriented at acute angles relative said each stack thereby forming a delamination interface.

[0005] This structure has a better or comparable blast resistance at equal or lower weight and has further potential advantages in reduced back-face deformation; high impact energy absorption; improved formability / manufacturability; improved corrosion resistance. The term "right angle" indicates an angle substantially perpendicular, but not excluding small deviations therefrom, e.g. in the order of plus or minus 10 degrees. An angle is measured as a smallest angle between 0-90 degrees, between unidirectional orientations of two intersecting fibre orientations. The term "acute angle" similarly indicates an angle about half of a right angle, so that the orientation of subsequent packed stacks is substantially mirror symmetrical.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figure 1 (A + B) shows an schematic embodiment of a stack layout;

Figure 2 shows a schematic embodiment of a package layout;

Figure 3 shows a graph of a blast results related to sheet layer thickness.

DETAILED DESCRIPTION

[0007] Military vehicles are designed to withstand serious impacts, e.g. of ballistic projectiles or explosions, e.g. of a mine below the vehicle. As a result, typically the vehicle is comprised of heavy and thick materials, to form doors, side walls and bottom walls of the vehicle, typical armor steel. This heavily impacts the weight of the vehicle which impacts mobility and versatility. A need exists to use lighter materials for blast and ballistic protection, resulting in better mobility characteristics at lower engine power, and lower required weight for e.g. the chassis, suspension, axes and transmission.

[0008] A composite material known as GLARE, is formed from thin glass fibre layers and aluminum layers. Other composites are based on carbon fibre or E-glass fibre. It is found that material and composite structure are leading properties for good resistance against blast impact. Glass fibres have a unique property that tensile strength and strain to failure increase in relevant dynamic conditions. For instance, compared to a static stress test, strain to failure for S2-glass increases from about 4.5% to about 6.5%. In addition, in relevant (blast) pressure conditions, the strain to failure and tensile strength even further increases to about 9% with a tensile stress of 8000MPa. Without being bound to theory, it is found that glass fibre composite materials that fail as a result of blast impact, experience a strain at failure, at the backside of the panel, that is higher than a limit threshold. It is concluded that a high threshold for tensile strength is important. To resist high pressure blast conditions, it is found that the sheet thickness needs to be sufficient, which in testing resulted in sheet preferably from about 0.3 to 1.1 mm, or more particularly, at least about 0.5 mm. Such thickness of sheets results in timely delamination of the sheet materials, which enables an increased pressure load on the material and that improves its tensile strength properties.

[0009] Furthermore, it is concluded that the use of unidirectional fibres is important for blast protection. Moreover, an important aspect, as presently disclosed is that, in addition to use of fibres having a high tensile strength and the use of relatively thick sheets of a unidirectional fibre orientation, the interface region between subsequent packed stacks of sheets is important.

[0010] Turning to Figure 1A, it is disclosed how a preferable orientation is of sheets within a packed stack 10 of two sheets 1, 2. In practice, the number of sheets is higher than 4. By way of example, it is shown how the packed stack 10 comprises fibre-reinforced resin sheets 1, 2 each with dominant unidirectional fibre orientations and stacked, within said each packed stack 10, alternatingly at about right angles relative to each other. In particular, in comparison with Figure 1B, it is shown that stack 10' with sheets 1 and 2 differ from stack 10 in that in stack 10, sheet 2 is not oriented at a right angle but at an acute angle. From the comparison of both stacks 10, 10' it becomes clear that the first orientation 10 is beneficial for orienting, in an impact situation, as straight as possible, by having transversely oriented fibres at about right angles, keeping the side impact (transverse to the longitudinal direction) as low as possible.

[0011] Going further, in Figure 2, it is now shown how this principle of right-angled sheet layout is applied to gain a more quasi-isotropic stack layout of a cluster 100 of m packed stacks 10, 10'. For practical purposes the number m typically ranges about 5-20. Each stack 10, 10' comprises fibre-reinforced resin sheets 1,2, 1', 2' with dominant unidirectional fibres oriented, within said each stack 10, 10', alternatingly at about right angles relative to each other. The stacks 10, 10' have a thickness, larger than about 1.5 mm, preferably about 1-4 mm, preferably larger than 2 mm, accounting for a number of n sheets with n larger than 4, ranging about 4-25.

[0012] A cluster 100 of stacks is at least formed by a stack 10 having fibre-reinforced resin sheets 1,2, with dominant unidirectional fibres oriented, within said stack 10, alternatingly at about right angles relative to each other; and a stack 10' having fibre-reinforced resin sheets 1',2', with dominant unidirectional fibres also oriented, within said stack 10' alternatingly at about right angles relative to each other; wherein said each stack packed between adjacent stacks, said adjacent stacks comprising sheets with dominant unidirectional fibres oriented alternatingly at acute angles relative said each stack. These acute angles may vary between 35 and 55 degrees relative to a dominant length orientation in stack 10; more in particular, sheets 1', 2' in stack 10' are oriented at plus and minus 45 degrees relative to a dominant length orientation in stack 10; whereas sheets 1,2 in stack 10 are oriented at 0 and about 90 degrees, i.e. ranging between 80 and 100 degrees relative to a dominant length orientation.

[0013] In the embodiment of Figure 2, sheets 1,2, 1', 2' are relatively thick, which means at least larger than 0.3 mm per sheet, in particular, about 0.3-1.5 mm, more specifically about 0.6 mm.

[0014] In particular, it is found that packed stacks of thick sheets are preferably stacked and said packed stacks comprising sheets with dominant unidirectional fibres are oriented, between subsequent packed stacks, alternatingly at an acute angle relative to each other, more particular at angles that are alternatingly plus and minus 45 degrees, for obtaining a quasi-isotropic fibre orientation. Thus a stack comprises fibre-reinforced resin sheets with dominant unidirectional fibres oriented, within said each packed stack, alternatingly at about right angles relative to each other (called a 0/90 degree orientation); and said packed stacks comprising sheets with dominant unidirectional fibres oriented, between subsequently stacked packed stacks, alternatingly at an acute angle relative to each other (called a +/- 45 degree orientation)

[0015] While, as explained with reference to Figure 1, this lay-up in principal negatively impacts the 'quasi isotropic' characteristics of a stack of packed stacks, surprisingly it appeared that such a clustered packed stacking of the sheets in each packed stack yields a unique new composite material with quasi isotropic properties that is better suited for blast protection than a typical 0/90/-45+45 stacking arrangement.

[0016] In particular, the sheets may be fabricated from main components, fibres and resin. The fibres are aligned in sheet material rolled onto rolls. When produced, the fibres, e.g. multiple S2 glass fibres bobbins positioned side by side are unwound and directed onto rolls, having a predetermined orientation. Subsequently, the fibres are rolled out onto or into a mould and said fibres are subsequently impregnated with resin, e.g. an epoxy resin and are processed under vacuum conditions, e.g. an autoclave.

[0017] Alternatively, pre-impregnated fibres may be used, obviating the impregnation step as herebefore described. After hardening, the composite sheet can be released from the mould and handled for further processing. Preferably, the fibre volume content is higher than 50% of the sheet volume.

[0018] In an example, a stack is characterized by relative thick sheets (>0.3 mm) stacked in a pattern within a packed stack, alternatingly at about right angles relative to each other, to packed stacks of about more than 2 millimeters thickness.

[0019] Without being bound to theory, the inventive blast protection panel is designed so that impact leads to a timed delamination between the subsequent packed stacks, so that the bending stresses in the material are reduced. In combination with a high tensile strength, e.g. of S2 glass that withstands high dynamic loads, this provides blast protection properties that are comparable and better than steel alternative.

[0020] Going forward, some embodiments will be described of the principle as illustrated hereabove with reference to Figure 2.
Package 1: 0/90/-45/+45/+45/-45/90/0
or
Package 2: 0/90/-45/+45/0/90/-45/+45/+45/-45/90/0/+45/-45/90/0 (underlined sheets denote the middle of the package).
These packages are characterized by a symmetric composition, i.e. going inward outer stacks are each stacked in corresponding same orientations from both sides of the panel. Furthermore, the number of 0/90 and +45/-45 stacks are the same; in Material 1 in 2 and 2 sheet layers respectively and in Material 2 in 4 and 4 sheet layers respectively. The stack interfaces having fiber orientations in acute angles is evenly distributed through the package. In the materials, the stacks each have a thickness of about 0.9-1.1 mm. However, in the example packages, not every and each stack comprises at least four fibre-reinforced resin sheets with fibres oriented, within said each stack, alternatingly at about right angles relative to each other; since in Package 1 stacks are formed of two sheets each and in Package 2 only one stack has at least four sheets (Package 2, middle stack)
Package 3: +45/+45/+45/0/0/0/90/90/90/-45/-45/-45/+45+45/+45/ 0/0/0/90/90/90/ -45/-45/-45/+45/0/90/-45/-45-45/-45/ 90/90/90/0/0/0/+45/+45/+45/ /-45-45/-45/ 90/90/90/0/0/0/+45/+45/+45/
(underlined sheets denote the middle of the package).
The short-handed lay-up is as follows
+45³/0³/90³/-45³/+45³/0³/90³/-45³/+45¹/0¹/90¹/-45¹/-45³/90³/0³/+45³/-45³/90³/0³/+45³
The number of sheets in each stack is still smaller than four.
The sheets in the stack are about 0.9 mm and are nicely delaminated in the blast, which is the desired effect.
However it is more desirable that the sheets within the stack are not delaminated, but that the stacks are delaminated on adjacent interfaces. When delaminating on sheet level, a propagation path can be formed for the blast, through delaminating sheets, which happens especially when sheets are oriented at acute angles relative to each other. This effect can be mitigated by providing clusters of stacks, each stack having a 0/90 orientation or a +45/-45 orientation; wherein the stacks are clustered to a stack thickness of at least four sheets in a stack.
Package 4: +45²/-45²/+45²/-45²/+45²/-45²/ 0²/90²/ 0²/90²/0²/90²/ 0¹/90²/0¹/ /90²/ 0²/90²/0²/90²/0²/ -45²/+45²/-45²/+45²/-45²/+45²
In this packages a first stack of 12 sheets is formed having a +45/-45 orientation. Then a stack of 28 sheets is formed having 0/90 fiber orientation and then another 12 sheets having -45/+45 fiber orientation. In this packages there are only a limited number of interfaces (only two) where the fiber orientation is at acute angles which reduces the number of interfaces where delamination takes place. The outer sides of the package, (+45/-45 stacks) will deform in another direction than the central 0/90 stack. Only two interfaces having acute angles relative to adjacent stacks will be loaded between three stacks. These two interfaces will be most sensitive to delamination. Conversely, the stacks within the packages will not exhibit internal delamination interfaces, due to the right angle orientation of the at least four sheets within the stack. Preferably, the sheet thickness are selected in a range of about 0.6 mm, and the stacks may be about 3 mm, for a total thickness of the package of about 15 mm.
Thus, in total a package of 52 sheets is provided to a thickness of about 15 mm having excellent blast resistant properties.
In a scaled up version a package can be clustered in 5 stacks, instead of 3 as earlier described.
Package 5:

+45/-45:	12 sheet layers	thickness = 3,6mm
0/90 :	18 sheet layers	thickness = 5,5mm
+45/-45:	12 layers	thickness = 3,6mm
0/90 :	18 layers	thickness = 5,5mm
+45/-45:	12 layers	thickness = 3,6mm

In total 72 sheet layers having a thickness of about 22mm
Package 6 has following stack layup:
+45³/0³/90³/-45³/ +45³/0³/90³/-45³/ +45³/0³/90³/-45³ - 45³/90³/0³/+45³/ -45³/90³/0³/+45³/ -45³/90³/0³/+45³

[0021] Here the number of interfaces having acute angles is increased relative to package 5. It is found that Package 5 performs better than Package 6.
In a further scaled-up package a stack layout may be

+45/-45:	12 layers	thickness = 3,6mm
0/90 :	12 layers	thickness = 3,6mm
+45/-45:	12 layers	thickness = 3,6mm
0/90 :	16 layers	thickness = 5mm
+45/-45:	12 layers	thickness = 3,6mm
0/90 :	16 layers	thickness = 5mm
+45/-45:	12 layers	thickness = 3,6mm
0/90 :	16 layers	thickness = 5mm
+45/-45:	12 layers	thickness = 3,6mm
0/90 :	12 layers	thickness = 3,6mm
+45/-45:	12 layers	thickness = 3,6mm

[0022] In total 144 sheet layers having a thickness of about 44mm.

[0023] In Figure 3, a graph is shown of a blast results related to sheet layer thickness. The graph shows for sheet layer thickness a critical distance relative to a standard blast load. It is found that a sheet layer thickness yields better results, as the critical distance is 60 mm, relative to a thickness of 0.9, having a critical distance of 80 mm - meaning that the package is destroyed at closer ranges.

Comparative example.

[0024] A test is conducted with two types of panels:
A T300-carbon weave / PEI resin panel with a thickness of 15 mm An E-glass weave / PEI resin panel with a thickness of 15 mm.

[0025] Both samples are tested with the 188 g Semtex explosive charge, positioned at varying distances between the charge face and the panel face. The charge is placed on a massive steel backing plate (thickness > 5 cm). The panels themselves are supported by an overdimensioned thick steel plate featuring a circular hole, through which the panel bulges inward under the effect of the applied blast pressure. The results can be found in Table 2.

[0026] From the data in the table, it becomes clear that nor carbon fibre-based nor E-glass composites using PEI resin could match the performance of e.g. aluminium. The maximum strain level in the carbon fibre-based composite would reach just 1.2% before failing, even at large charge-to-panel distance. In an video analysis it becomes apparent that failure occurs during the very first instance of panel deformation. At this early stage, the blast pressure only affects a small region at the center of the panel, resulting in very local bending. Carbon fibre does not possess the necessary strain-to-failure to accommodate this local initial panel bending, and there is little help from strain rate effects.

[0027] For the E-glass based composites, better results were obtained. From highspeed video analysis it can be observed that the critical deformation resulting in exceedance of the strain to failure due to local bending is significantly increased, yet it is still significantly lower than for aluminium. Although E-glass is weaker than carbon fibre in terms of tensile strength, E-glass has a higher strain to failure. As such, a next panel would ideally combine properties of aluminium and an even stronger type of glass fibre.

[0028] Without being bound to theory, it is believed that the use of weave-like fibres, such as the carbon and E-glass used in this experiments, will lead to stress concentrations at the overlap points between fibres, and as a result it is to believed that the use of unidirectional (UD) fibre layers is beneficial

[0029] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs as read in the context of the description and drawings. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. In some instances, detailed descriptions of well-known devices and methods may be omitted so as not to obscure the description of the present systems and methods. Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and/or" includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms "comprises" and/or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

[0030] While example embodiments were shown for systems and methods, also alternative ways may be envisaged by those skilled in the art having the benefit of the present disclosure for achieving a similar function and result. E.g. some components may be combined or split up into one or more alternative components.

[0031] It is not excluded that the delamination interfaces are provided by acute angles differing from 45 degrees. In practical embodiments, depending on purpose, the numbers of sheets and stacks may vary, and the invention is not limited to the disclosed examples. The sheets may also vary in thickness. Also, further composites may be formed including metal layers.

[0032] For example, the above-discussion is intended to be merely illustrative of the present system and should not be construed as limiting the appended claims to any particular embodiment or group of embodiments. Thus, while the present system has been described in particular detail with reference to specific exemplary embodiments thereof, it should also be appreciated that numerous modifications and alternative embodiments may be devised by those having ordinary skill in the art without departing from the scope of the present systems and methods as set forth in the claims that follow. The specifications and drawings are accordingly to be regarded in an illustrative manner and are not intended to limit the scope of the appended claims.

[0033] In interpreting the appended claims, it should be understood that the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim; the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements; any reference signs in the claims do not limit their scope; several "means" may be represented by the same or different item(s) or implemented structure or function; any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A blast protection panel, comprising a package of fibre-reinforced resin sheets, each sheet having a dominant unidirectional fibre orientation, said package of fibre-reinforced resin sheets formed in packed stacks, each stack comprising at least four fibre-reinforced resin sheets with fibres oriented, within said each stack, at about right angles relative to each other; and said each stack packed against an adjacent stack, said adjacent stacks comprising sheets with dominant unidirectional fibres oriented at acute angles relative said each stack thereby forming a delamination interface.

2. A blast protection panel according to claim 1, wherein the panel is formed integrally or attached to a compartment, e.g. a vehicle compartment.

3. A blast protection panel according to any preceding claim, wherein the right angles vary between 80 and 100 degrees, more in particular about 90 degrees.

4. A blast protection panel according to any preceding claim, wherein the acute angles vary between 30 and 60 degrees, more in particular, 40 and 50 degrees, more in particular about 45 degrees.

5. A blast protection panel according to any preceding claim, wherein the panel is curved, in particular shaped as a non-flat panel.

6. A blast protection panel according to any preceding claim, wherein a packed stack measures a packed stack thickness of about 1-4 mm, more specifically larger than about 2 mm.

7. A blast protection panel according to any preceding claim, wherein a sheet measures a sheet thickness of about 0.3 -1.5 mm, more specifically about 0.6 mm.

8. A blast protection panel according to any preceding claim, wherein the number of sheets within each stack having fibres oriented, within said each stack, alternatingly at about right angles relative to each other, ranges between 4 and 25.

9. A blast protection panel according to any preceding claim, wherein the number of stacks, of fibre-reinforced resin sheets formed in packed stacks, in the package ranges between 3 and 30, more specifically between 5 and 15.

10. A blast protection panel according to any preceding claim, wherein the fibres are glass fibres, in particular S- glass or S2 glass.

11. A blast protection panel according to any preceding claim, wherein the fibres have a fibre volume in the sheets higher than 50%.

12. A blast protection panel according to any preceding claim, wherein panel is about 1-6, more specifically 2-4 cm thick.

Drawing